This invention relates to mechanism for applying protective coating to selected surface portions and/or fractures therein, especially the fractured localities of easy-open sheet metal lids or the like.
The above cited patents are concerned with easy-open end closures for sheet metal cans. As therein disclosed a can lid is formed with a disruptable button portion defined by merging inner and outer wall portions inclined to the general plane of the lid. One of the walls is longitudinally indented in a coining operation while backed by a curved die surface thus preferably producing a fracture through the metal and extending roughly from about 120.degree. to 180.degree. peripherally. The locality of no indentation, generally opposite to the locality of greatest indentation and fracture, serves as a hinge for the closure when the button portion is pressed inwardly, and the fracture serves as an easy starting locality for the rupture. For insuring that the button portion adequately resists internal pressure, for instance such as may be generated by carbonated beverage or in the pasteurizing of beer, etc., a face of the indentation is dilated, as by a swedging step, relative to the fracture and yet permits closure disruption manually from outside the container.
Can lids of the general type indicated are customarily made at high speed on in-line, multi-station forming apparatus. The lids are usually conveyed sequentially as by endless belt to and through the forming and treating stations. While the precision forming and swedging generally produce uniformly fractured lids, there is variation inevitably in the sheet metal from which the lids are produced, and hence it is desirable to provide one lid making station at which the successive lid closures have their fracture rendered fluid tight with certainty and without modifying the substantially uniform can opening or rupturing force required. Moreover, sealing equipment of the type herein to be disclosed may well have application in the high speed production of can lids of different configuration and construction and whenever an economical coating for sealing and/or anticontamination is desired. Also, this invention has application in can making where, because of partial breakdown of a prior coating in a locality due to operation thereon of a scoring tool or the like, a local re-coating is required.
In the prior art, for example as shown in U.S. Pat. No. 3,807,924, it is known to employ injectors for delivering batches of fluid plastic material, for instance to the interiors of caps. Also, in the making of can lids it is a common practice to spray a coating of lacquer or the like on one surface. Another known approach employs application of hot-melts or lacquers by direct contact. According to one system, for instance, a plurality of spaced, tiny globules of cement are deposited around the perimeter of a push-in closure; then the cover is placed in a hot oven to cause the globules to run together to form a continuous seal.